I have had multiple users request this in Armory.  My response is controversial, but I want to throw it out there as food for thought, and you can ignore it if you don't like it:

If you have an encrypted wallet and all your backups are encrypted as well, including encrypted paper backups -- you have a brain-wallet.  Not exactly a brain-wallet, just all the downsides of brain-wallets.  You are at significant risk of losing your coins no matter how good you think you are.  Either because you forget your encryption passphrase because you only used it once five years earlier when you made the backup, or because you get hit by a bus and take the passphrase (and BTC) to your grave with you.  If the encryption is implemented properly, the backup will be useless without the passphrase.

I have no problem with having encrypted backups in addition to an unencrypted backup stored somewhere secure such as a safe or safe-deposit box.  But I think if the option is there, a lot of users will make 100% of their backups encrypted, and a lot of BTC will be permanently lost.